The development of non-lethal projectiles for firearms in recent times for use in violent and criminal situations has been addressed primarily with the design and material of a soft slug in order to soften the impact of the slug to a non-lethal level. Soft slugs such as "rubber bullets" have long been used with conventional thrust systems of chemically-reactive powders and substances to create a cartridge for use in conventional guns, especially small arms such as rifles, shotguns, pistols and revolvers. The use of such propellants have several disadvantages including toxic chemical fumes, loud report, large shock waves, and a non-variable thrust which cannot be modified to meet the need for non-deadly use at close ranges or with smaller targets. The current conventional non-lethal bullets are made of some soft material such as rubber, plastic or foam. Other non-lethal projectiles or slugs have been described as bean-bags, sand-bags, foam bullets and the like. But even these projectiles can be deadly at close range and with smaller human targets. A slug for which the velocity and thus the impact can be modified to match a variety of desired non-lethal applications has long been needed. The present invention addresses the problem from the standpoint of the propulsive system itself and not the slug or projectile, thereby meeting this need by providing a variably and selectably controlled propulsive system.